(1.) Field of the Invention
The present invention relates to means for suppressing vibration and structureborne noise propagation in piping systems.
(2.) Description of the Prior Art
It has been found that flow-induced noise and vibration in piping systems or any other cylindrical structures results primarily from the coincidence of bending waves in the wall of the pipe structure and from internal acoustic modes. In order to reduce this vibration and structureborne noise, a number of techniques involving a combination of axial and circumferential stiffeners have been utilized. One such technique is known as constrained layer damping in which the pipe, duct or cylindrical shell is wrapped with an elastomeric material over which is wrapped a metallic sheet material, the two layers being held in place by means of a series of axially spaced steel bands. Another existing technique is known as stave damping-in which the pipe is once again wrapped with an elastomeric material, said layer then being covered with a plurality of elongated metal staves extending axially along the pipe, the assembly then being held in place by a series of axially spaced steel bands. A further technique, known as the tuned absorber method, is actually similar to stave damping except that the elongated metal staves are in spaced relation to each other.
Other techniques comprise the use of high damping alloys, i.e., the pipe or duct is actually constructed of an alloy that inherently exhibits damping characteristics. Still another technique utilizes composite materials wherein the pipe or duct is covered with wound carbon fibers, over which there is provided a coating of carbon impregnated resin.
Although all of the above techniques are somewhat effective for their intended purpose, they nevertheless have serious disadvantages. For example, constrained layer damping, stave damping, tuned absorber, and the use of high damping alloys are costly, bulky, and heavy, and although the use of composite materials is not as heavy and bulky, it is difficult to use this technique, as it is with all of the others, on ducts or pipes that do not have a constant diameter. In other words, none of these prior art techniques are effectively usable where the pipe or duct has an irregular surface, such as a plurality of different diameters caused by steps or shoulders along the length of the pipe. Also, all of these prior art techniques provide a uniform damping along the entire length of the pipe, whereas it is obviously more desirable to be able to specifically locate damping means at the dominant axial wave locations of the pipe, i.e., the specific areas along the length of the pipe where damping is most required.